Head-up displays are display devices, which can be used to project information into view through a vehicle window in vehicles such as for example passenger vehicles, utility vehicles and also rail vehicles. Head-up displays in particular generate virtual images of the information to be presented, which appear to be located in front of the vehicle window, such as for example a windscreen. This offers the advantage in particular for vehicle operators that they hardly have to gaze away from a visible traffic situation in front of the vehicle when viewing displayed information, as is necessary in the case of displays on a traditional instrument panel. In addition, the displayed information is perceivable without refocusing the eyes, because the virtual image thereof appears to be located in front of the vehicle window.
Generally speaking, two principally different types of head-up displays for motor vehicles are known. One is the head-up display which projects an image that is generated by an image generating and imaging device onto the internal side of a windscreen, which serves as a reflection surface and reflects the projected image to a viewer. The viewer can perceive the image that is generated by the image generating and imaging device as an imaginary image located behind the windscreen, as viewed by him. Such a head-up display is described, for example, in U.S. Pat. No. 5,486,840.
The other type of head-up display uses not the windscreen as a reflection surface, but a separate combiner screen arranged between a viewer and a windscreen of the motor vehicle, wherein the combiner screen serves as the reflection surface and reflects the image that is generated by the image generating and imaging device to the viewer, who perceives the image thus generated as being located behind the combiner screen, as viewed by him, generally also behind the windscreen, which is arranged behind the combiner screen, as an imaginary image. Such combiner head-up displays are known for example from JP 4940850 B2, JP H10138794 A and U.S. Pat. No. 5,867,287.
A head-up display that combines a combiner element with a windscreen by way of the fact that the windscreen has a reflective beam splitter coating on its internal side is disclosed in U.S. Pat. No. 5,053,755.
One general disadvantage of the combiner head-up displays with respect to the head-up displays first mentioned is that, owing to the light-transmissive property of the combiner screen, the person viewing the head-up display can also perceive through said combiner screen undesired reflections on the windscreen of the vehicle, which can occur for example if ambient light that is incident from outside the vehicle, such as sunlight, is reflected toward the internal side of the windscreen by elements such as for example ventilation slots or edges of an instrument panel. Such reflections on the windscreen can negatively affect the viewer's perceived visual impression through the combiner screen significantly.
Against this background, the present disclosure is based on the object of providing a head-up display for a vehicle, which permits a viewer better visibility and perception of the information displayed by the head-up display.